Well, that doesn't make sense either! Each update gets cheaper? I'll believe it when I see it, because it's not logical. You maintain my confusion!
Look. Version .5 comes out. For a week or 2, it costs 25. For a week after that it's cheaper, because it's not immediate. Then cheaper still. then update .6 comes out and you can download update .5 for free. And like I said, this information is in the log of some of the devs older games on this site. Just look through those and you'll have a more precise description of the process. Either way, the payment is optional. Many devs work like this, you can pay for the fresh new content, (which funds future production of the game), or you can just wait a month for when it becomes free because there's a newer update. True this is a higher than average price, but it's still the same process as most other adult game developers.